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Quadraphonic


dtr20

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On ‎6‎/‎26‎/‎2017 at 3:09 PM, babadono said:

Sending the same L and R signals to a rear pair of speakers will just make a lot of noise. It will ruin the stereo image of the front speakers. Just MHO

If the album/material is true CD-4/Discrete, it is NOT the same signal going to the rear speakers.  In CD-4/Discrete, the rear channels' material which was "re-modulated" to a higher frequency band above the human range of hearing then put onto the vinyl; then...when played those channels go thru a "demodulator" and the material which was re-modulated to the frequency band above the human range of hearing revert back to their original band of frequencies and come out through the rear speakers.  The demodulator has a built-in time-delay so that the front channels' signals come out of it at the same time as the rear channels' signals and there is no "time distortion" to what you hear (due to the micro-millisecond(s) taken up in demodulation process of the rear frequencies)...and everything is fired into the quad pre-amp section simultaneously so that it all comes out thru the speakers timed correctly.  Listening to CD-4/discrete vinyl CAN BE some amazing experience(s), if it is produced/recorded correctly!   

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On 10/17/2016 at 3:25 PM, dtr20 said:

My father @TomR recently got a Pioneer qx-949 quadraphonic receiver. He remembers in the 70s certain fm stations would broadcast in quadraphonic on Sunday night's only. We really want to experience quadraphonic, but we have no clue about it. We know there were turntables made, but they seem to cost a lot and still need work it replacement cartridges, etc. We don't want to spend a lot of money because we have a hunch that it will be very underwhelming. I know someone that has a quadraphonic reel-to-reel, but he didn't know anything else about quadraphonic. 

 

Any information that you guys might have would be helpful. We know we could always take Y splitters on the rca's from a 2 channel source and get the signal to all 4 speakers that way. Thanks guys

 

On 6/26/2017 at 0:09 PM, babadono said:

Sending the same L and R signals to a rear pair of speakers will just make a lot of noise. It will ruin the stereo image of the front speakers. Just MHO

 

4 minutes ago, HDBRbuilder said:

If the album/material is true CD-4/Discrete, it is NOT the same signal going to the rear speakers.  In CD-4/Discrete, the rear channels' material which was "re-modulated" to a higher frequency band above the human range of hearing then put onto the vinyl; then...when played those channels go thru a "demodulator" and the material which was re-modulated to the frequency band above the human range of hearing revert back to their original band of frequencies and come out through the rear speakers.  The demodulator has a built-in time-delay so that the front channels' signals come out of it at the same time as the rear channels' signals and there is no "time distortion" to what you hear (due to the micro-millisecond(s) taken up in demodulation process of the rear frequencies)...and everything is fired into the quad pre-amp section simultaneously so that it all comes out thru the speakers timed correctly.  Listening to CD-4/discrete vinyl CAN BE some amazing experience(s), if it is produced/recorded correctly!   

Roger that @HDBRbuilder. True multi channel audio can and does sound good when done properly. Witness everybody having 5.1 and 7.1 and now what is it 9.2.4 or some such home theater set ups. I was just commenting on the OPs original statement that in MHO, sure you can increase the volume of the soundfield by adding amps and speakers. But don't be looking for a good stereo image.

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2 minutes ago, babadono said:

 

 

Roger that @HDBRbuilder. True multi channel audio can and does sound good when done properly. Witness everybody having 5.1 and 7.1 and now what is it 9.2.4 or some such home theater set ups. I was just commenting on the OPs original statement that in MHO, sure you can increase the volume of the soundfield by adding amps and speakers. But don't be looking for a good stereo image.

AGREED!  Y-splitters are not quad!  Even the SQ and QS matrix 4-channel is NOT REALLY quad...it is SIMULATED quad, at best...depending on the matrix type and version of it (they tended to change to some extent over the time quad matrixes were in use)...the carrier signal was supposed to cause the matrix decoder to send certain frequencies/material to the rear channels, which tended to cause those rear channels to generally become more of a REVERB type thing than true 4-channel, unlike CD-4/discrete. 

 

Two caveats about CD-4 are that the internal wiring of the turntable was/is also important...from the cartridge thru to the cables/connectors of the turntable, MOST turntables commonly used in those days had no problems, but some did, in handling the higher frequency bands used for CD-4 rear channel signals...but the most important thing was having a quality CD-4/Discrete CARTRIDGE/Stylus combo that could initially pick up the much higher frequency band for the rear channels.  Downstream from the turntable was not an issue if the preamp or reciever had a properly calibrated demodulator in it or an outboard demodulator plugged into it between the turntable and the preamp/preamp section (for receivers).

 

Technics turntables were ready for CD-4 from day one, even the earliest ones. whereas SOME other manufacturers had to "play catch-up" to get what they were already manufacturing into the CD-4 game.  If you ever wonder why, all of a sudden, some companies came out with different turntables during the time between the introduction of CD-4 and its waning, that is generally the reason why those models were introduced by those companies...and many of them were just "electrical circuit" and/or head-shell upgrades to an already existing model.  Thorens comes to mind, and Empire, Dual and a few others.  Some changes were designated as "totally" new models, but many were just given a Roman "II" or Mark whatever as an improved model which had already existed previously within in their turntable line-ups.

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I never wanted to use y splitters to send the signal to the rears, I wanted to address this so people wouldn't suggest it to us. I just picked up a Pioneer pl-55dx turntable that is capable of true cd-4. @HDBRbuilder, can you suggest a quality CD-4 to look for? Thanks

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36 minutes ago, dtr20 said:

I never wanted to use y splitters to send the signal to the rears, I wanted to address this so people wouldn't suggest it to us. I just picked up a Pioneer pl-55dx turntable that is capable of true cd-4. @HDBRbuilder, can you suggest a quality CD-4 to look for? Thanks

Are you asking for suggestion for an album or a cartridge/stylus combo, or what?

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I will likely have much more to say on this in the not too distant future, as I have some support based on my results to indicate that correctly recorded surround does what one would intuitively suspect:  Get closer to accuracy more than twice as good as stereo does over mono.

 

For the moment, I'll say this for you to think on:  Most agree that the very best stereo is produced from two properly placed microphones direct to storage a la the legendary Living Presence and others and reproduced on two properly placed speakers. 

 

IF you accept that, then does it not follow that 4 microphones properly placed, recorded, and played back the same way would be even more accurate and immersive? 

 

I will offer this much.  My experience is that the above is true, but the achievement of the expansion from two to four microphones is NOT as simple as adding two more in mirror image...but can be done. 

 

Dave

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Rick Wakeman's Six Wives of Henry VIII Quad LP was what my neighbor had in the late 70s right before "Some Girls" came out. I had a Panasonic out of one box with the record player 8-track, fm radio and two speakers. His was a quadrophonic with four speakers don't recall the brand but that instrumental you could hear the keyboards circling the room. Like a BOC concert when they do the "Godzilla" footsteps out travelling around in the mezzanine of the coliseum. 

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4 minutes ago, dtr20 said:

An album please

Jethro Tull, Aqualung; ELP, Brain Salad Surgery; Joni Mitchell, The Hissing of Summer Lawns...what kind of music are you into?  All of my CD-4 albums are old stuff from when CD-4 was actually happening.  Some sound great and some that DO sound great are almost an "exercise in sound effects"...most of those were recorded specifically to be released in Quad, though...and in stereo you lose some of the intent which drove the process when it was mixed down from the masters.

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2 hours ago, JohnJ said:

Rick Wakeman's Six Wives of Henry VIII Quad LP was what my neighbor had in the late 70s right before "Some Girls" came out. I had a Panasonic out of one box with the record player 8-track, fm radio and two speakers. His was a quadrophonic with four speakers don't recall the brand but that instrumental you could hear the keyboards circling the room. Like a BOC concert when they do the "Godzilla" footsteps out travelling around in the mezzanine of the coliseum. 

Almost anytime a cd-4 album was released back in the quad heyday, and was recorded and mixed down specifically for CD-4...AND IF an organ with a Leslie speaker was part of the mix, it was generally expected to be a "mind-altering experience assistant"...LOL!

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Actually, in CD-4, the front channels and the rear channels are the same quality. During the encoding process, the front channels are mixed with the rear channels in phase and recorded as the main audio on the audible part of the bandwidth. In this way, if you played it on a stereo system, you would experience it as a stereo record, and all the musical elements would be there with left/right separation maintained by vector modulation same as stereo. The subcarriers, there were two, one for each of the two channels, were separated and sent to two channels of demodulation. After demodulation there was ANRS noise reduction, a system similar to Dolby B. These subcarriers are the difference signal generated by mixing the front and rear channels out of phase, this is the separation information that is used to reconstitute the original four channels. To do that, the separation signal is mixed in phase with a sample of the main signal, and the rear signal is canceled out because it was out of phase when mixed in the modulator. This leaves only the front channel which is sent to the output. To get the rear channel, the same two signals are mixed, but the separation signal is mixed out of phase, so that the front channel audio is cancelled out leaving the rear channel signal which is sent to the output. Never are the left and right sides intermingled. So the result is that all four channels are the same quality.And the quality can be pretty good with the right setup. There is delay compensation in the modulator designed to correct for the natural delay in the demodulator. This was done to make the demodulators less expensive because they would not need to have their own compensation. CD-4's best performance was finally realized after the quad era, with the development of the microline stylus, or linear contact, a Shibata variant that performed better at tracking the finer modulations of the subcarrier frequencies. The CD-4 system is similar to FM stereo, except that FM stereo does not use noise reduction for the subcarrier.

 

With SQ and QS and other matrix systems, the left and right channels are intermingled, but they do start out as four independent channels. The encoders mixed the four channels into the two channels of stereo at different phase angles, which the decoder would try to extract. The problem was that the decoders could extract some separation, but not enough. It wasn't until the Tate system was developed that serious separation performance was realized for SQ, and Variomatrix for QS, but by that time, quad was commercially dying. It also didn't help that every cheapo stereo manufacturer had a fake quad system which consisted of a stereo with a Hafler circuit and a "quad" button, that made it sound different, but wasn't true quad.Many people thought they had heard quad, but never did.They were disappointed, of course.

 

The Quadfather

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